Self brazing material and a method of making the material

ABSTRACT

The invention is directed at a self-brazing strip. In an aspect, a process is used to generate a multi-layer alloy strip made up of at least one base layer of with a least another layer of material, that when both the material and base layer are brazed, form an alloy. In an aspect, the other layer of material can include a metal. The base layer can include titanium or a titanium alloy.

CLAIM OF PRIORITY

The present application claims priority from U.S. patent applicationSer. No. 15/137,361, filed Apr. 25, 2016, which claims priority to U.S.Provisional Patent Application No. 62/152,636, filed on Apr. 24, 2015,the disclosures of which are relied upon and incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

The present invention generally relates to processes of formingself-brazing materials. Specifically, the present invention relates toself-brazing materials where different metals, such as titanium, areused as a base material in the constituent composition (e.g. Ti-Basedmaterial).

BACKGROUND OF THE INVENTION

Generally, brazing (including titanium brazing) involves expensive brazecomponents where the cost is driven by the type of metal used, partcomplexity and end use requirements.

Traditionally titanium has been brazed either with clad TiCuNi foils orTiCuNi in the powder form. Both processes involve stacking layers oftitanium (base metal) with intermittent braze foil/powder and brazing ina highly controlled atmosphere. Such processes have a complicatedassembly operation, long assembly time and high yield losses combinedwith use of expensive vacuum furnaces. The additional actions requiredin individual stacking the base material and filler metal renders theoverall brazing process difficult to automate. Further, individuallystacking the base material and filler metal is significantly timeconsuming and often results in a poor intimate contact between the basemetal and the filler material, producing poor braze quality and failedparts. Poor contact between a braze filler and base material can alsocause oxidation of surface material which degrades the overall brazequality. Such issues often cause a significant loss in the overall yieldof the brazed material. Therefore, there is a need to address thedescribed challenges.

SUMMARY OF THE INVENTION

The present invention is directed at a method for producing a titaniumalloy self-brazing strip or other applications that contain fillermetal-base metal combinations which allow extracting desired brazeconstituent elements from the base metal to perform an in-situ brazealloy during brazing. In an aspect, other braze filler metalcombinations can be used.

These and other aspects of the invention can be realized from readingand understanding of the detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic representation of a cross-sectional viewof a cladded product according to an aspect of the current invention.

FIG. 2 illustrates a schematic representation of a cross-sectional viewof a cladded product according to another aspect of the currentinvention.

FIG. 3 illustrates a cladding process according to an aspect of thecurrent invention.

FIG. 4 illustrates a flow diagram of a process according to an aspect ofthe current invention.

DETAILED DESCRIPTION OF THE INVENTION

The new process for creating a self-brazing product is described herein.More specifically, a self-brazing alloy strip is created from theprocess. In effect, a base is joined with another or multiple layer(s)of different materials that can be later brazed, as shown in FIGS. 1-2.Each strip/foil of the self-brazing product includes discrete layers.When the self-brazing product is brazed, then the alloy is formed.

In an aspect, the multi-layer product comprises at least one metal baselayer that is joined with at least another layer of metal. In anexemplary aspect, the multi-layer product comprises at least one baselayer of titanium (Ti) or titanium alloy that is joined with at leastanother layer of metal that, when both layers (i.e., the base and otherlayer) are brazed, form a titanium alloy. In reference to the Ti baselayer product, each strip/foil of the self-brazing product comprisesdiscrete layers. In an exemplary aspect, the other metal can includecopper (Cu), nickel (Ni) or Zirconium (Zr). The layers are selectedaccording, but not limited, to: (a) brazing temperature (e.g. Zr can beadded as an extra layer as melting point depressant)—for lower preferredbrazing temperature; and (b) ease of bonding—just one layer can be usedto braze. In an aspect, the multi-layer titanium alloy strip can includeat least one base layer of titanium (or titanium alloy) along withmultiple layers of other metals. The combination of the base layer oftitanium and at least one other layer of metal creates a multi-layertitanium alloy self-brazing strip, as shown in FIGS. 1-2.

While the exemplary aspect above focuses on a self-brazing product thathas a base material of titanium/titanium alloy to form a titanium alloywhen brazed, other base materials, as well as other materials in theother layers, can be used. However, it should be noted that theplurality of layers and base material can include any desired metal ormetal alloy sufficient for achieving end product goals. Table 1 detailssome ideal braze filler metals according to possible base material (e.g.metal) combinations.

TABLE 1 Braze filler metal by base metal combination Braze Filler MetalChemical Composition Base Material BAlSi Silicon (6 to 13%) Aluminum andremainder Aluminum aluminum alloys BCu Phosphorus, Silver and Copper andcopper alloys remainder Copper BTi See above Titanium Base alloys

The additional layers are bonded to the base layer through variousmeans, as discussed below. In an aspect, the other materials can befound on either one side (see FIG. 1) or both sides (see FIG. 2) of thebase layer. In an aspect, a decision to include a metal on either sideof the base layer of the product is based on the end use of the product.In the case of layers on only one side, care needs to be taken to avoidoxidation of the exposed base metal, which can be accomplished by goodcontrol of the atmosphere in the brazing furnace.

FIGS. 1-2 provide example of the resulting strip/foil according toaspects of the present invention. As shown in FIG. 1, the base layer canhave another at least one other layer (layer 1 and 2) joined to oneside. As shown in FIG. 2, the base layer can have at least one otherlayer (layer 1, 2, 3, and 4) joined to either of its sides.Specifically, the other layers (layers 1, 2, 3, and 4) cansandwich/surround the base layer, with layers 1 and 2 being oriented onthe upper surface of the base layer and layers 3 and 4 being oriented onthe lower surface of the base layer. While FIGS. 1-2 show onlycombinations of two layers being added to a respective side, othervarious combination of number of other layers can added to the baselayer.

In an aspect, when the self-brazing product is configured to produce atitanium alloy, the strip/foil can include, but are not limited to, thefollowing combination of materials in layered order: Cu/Ti/Cu, Ni/Ti/Ni,Ni/Ti/Cu, Cu/Ti/Ni, Cu/Ni/Ti/Ni/Cu, Ni/Cu/Ti/Cu/Ni, Ni/Cu/Ti/Cu/Ni,Cu/Ni/Ti/Cu/Ni, Zr/Cu/Ti/Cu/Zr, Zr/Ni/Ti/Ni/Zr, Zr/Ni/Ti/Cu/Zr,Zr/Cu/Ti/Ni/Zr, Zr/Ni/Ti/Ni/Cu, Zr/Cu/Ti/Cu/Ni, Ni/Cu/Ti/Cu/Zr, andCu/Ni/Ti/Cu/Zr among other combinations.

The bonding of the material can be done through a clad approach, such asa roll bonding application, as shown in FIG. 3. In an aspect, otherbonding/cladding techniques may be used to produce a clad/bond ofdifferent metals, such as, but not limited to, hot roll bonding, coldroll bonding, explosion bonding, vacuum bonding, and laser cladding.Although various techniques of cladding can be used to produce themultilayer self-brazing product, a cold roll bonding is the preferredmethod for metals (e.g., titanium, aluminum, etc.) that oxidize quicklyat high temperatures and form stable oxides that are detrimental toachieving a good bond between the layers. A good bond is desired becausea weak bond will result in a weak braze. By cladding the multiple layerstogether, the addition of the layers or powders need not be done as aseparate step in the manufacturing process.

FIG. 3 illustrates a roll bonding operation to form the self-brazingalloy product. In an aspect, the roll bonding operation joins a baselayer with a plurality of other layers of material. In an aspect, theplurality of other layers can comprise just one additional layer. Inother aspects, the plurality of other layers can comprise two layers,one layer to be joined to each side of the base layer. In an exemplaryaspect, as shown in FIG. 3, the process can include a base layer andfour other layers (first layer, second layer, third layer, and fourthlayer) that surround the base layer. However, as discussed above,various numbers of layers can be used. The layers are selectedaccording, but not limited, to: (a) brazing temperature (e.g. Zr can beadded as an extra layer as melting point depressant)—for lower preferredbrazing temperature; and (b) ease of bonding—just one layer can be usedto braze.

FIG. 4 illustrates the process of producing the self-brazing materialfor manufacturing purposes. First, the multiple layer self-brazingproduct is formed by bonding/cladding the layers (step 100). Next, thecladded multi-layer product can be cut or formed into the parts neededfor the ultimate manufactured purpose (step 200). Lastly, the parts arethen brazed with one another (step 300).

FIG. 3 illustrates a manner in which step 100 (bonding/cladding thelayers via cold rolling) is carried out. However, as discussed above,various other bonding/cladding methods can be employed. In an aspect,the self-brazing multi-layered product can be formed into strips orfoils, depending on the end application. In an exemplary aspect forcreating a self-brazing titanium alloy product containing copper and/ornickel, the multi-layer product is readily rollable to foil gauges(0.002 inches) with no intermediate heat treating or annealing. In anaspect, if an intermediate anneal is desired/necessary before formingthe parts that need to be brazed, the process needs to be carefullycontrolled to avoid the formation of Kirkendall (i.e. because copper andnickel mix readily to form Kirkendall voids). Kirkendall voids can provedetrimental to subsequent forming operations.

Kirkendall voids form at temperatures above 1200 F (650 C) for theCopper-Nickel binary phase system. As such, the post heat treatmentshould ideally be set at 1200 F or lower. In an aspect, although thetitanium will not be completely annealed at temperatures of 1200 F orlower, it should be sufficiently stress relived to enable furtherforming operations. It should be noted that, during heat treatment(i.e., the treatment of the multi-layer product before brazing), copperand nickel will mix and alter the chemistry of the product duringbrazing.

Once the multi-layer product is formed (See FIGS. 1-2 for example), themulti-layer alloy strip can then be cut and/or formed into the variouspieces needed for manufacturing purposes (step 200). Various methods ofcutting and forming can be used for the desired pieces to be formed withthe limitations mentioned above for the operating temperature.

After the needed pieces/components/parts have been made from theself-brazing alloy strip, the components can then be placed together inthe desired orientation and brazed to join the components together (step300). When the brazing occurs, a small amount of the base material canbe drawn into the other layers of materials, producing an in-situ braze.Such a process of drawing the base material into a braze joint avoidsstacking layers of brazing fillers which contains the base materialnecessary for brazing, thus producing a more intimate contact and betterbraze quality. For example, when the base includes titanium and theother layers include nickel or copper alloys, a small amount of thetitanium from the base can be drawn into and mixed with the copper andnickel layers.

After carefully selecting the composition and brazing temperature, abraze joint can be achieved, drawing a small amount of titanium from thebase metal, by mixing the base metal with the filler metals such as Niand Cu. The result is an in-situ braze product. For example, to producea brazed 0.050 inch titanium product with a ratio 15 wt % Cu, 15 wt % Niand 70 wt % Ti (which is a commercially available braze composition)available at the interface, the bonded layers will have thicknessmeasurements of 0.00075 inches Ni and 0.00075 inches Cu on both sides ofa 0.057 inch layer of titanium. During the brazing process, 0.007″inches of titanium will go into the brazing, resulting in a 0.050 inchlayer of titanium. The brazing temperature is between 1785 F (975C)—1922 F (1050 C). As previously mentioned, the brazing temperaturemust be carefully controlled because a change in brazing temperature canresult in a change in the in-situ braze alloy which can in turn changethe amount of titanium extracted from the base metal.

While U.S. Pat. No. 7,527,187 discloses a brazing of a foil to the basematerial (Ti), the process described above utilizes the base material(e.g., Ti) in the brazing process. In other words, instead of adding abrazing alloy to the base material, the base material is used to formthe brazing alloy.

Metals like titanium are reactive and combine with oxygen, carbon,hydrogen and nitrogen readily. As such, it is imperative that highlycontrolled vacuum furnaces are used to braze exposed titanium products.In an aspect, results from the present invention indicate that thecarbon in the graphite elements react with the titanium and formbarriers for an ideal braze. Cladding multilayers on both sides of thebase titanium avoids exposure to atmosphere which in turn enables theuse of furnaces that are less expensive and have less controlledatmospheres.

The products made after the brazing can be used in a variety ofoperations, including, but not limited to, high volume manufacturingoperations, such as the production of heat exchangers, brazed bellowsand honeycomb structures. By creating the self-brazing alloy product,there is no need for brazing foils, fluxes and powdered products in thejoining phase.

Having thus described exemplary embodiments of a method to producemetallic composite material, it should be noted by those skilled in theart that the within disclosures are exemplary only and that variousother alternatives, adaptations, and modifications may be made withinthe scope of this disclosure. Accordingly, the invention is not limitedto the specific embodiments as illustrated herein, but is only limitedby the following claims.

What is claimed is:
 1. An in-situ synthesized brazed product, comprising: a base layer of a first material comprising titanium or titanium alloy; and at least one other layer of a second material comprising copper, nickel, and/or zirconium, wherein the base layer of the first material is bonded to the at least one other layer of the second material, wherein some of the base layer of material is configured to interact with the at least one other layer of the second material upon applying brazing between approximately 1785° F. to 1992° F.
 2. The in-situ synthesized brazed product of claim 1, wherein the brazed alloy is formed in-situ during brazing by extracting the first material from the base layer.
 3. The in-situ synthesized brazed product of claim 1, wherein the at least one other layer of the second material comprises a plurality of other layers.
 4. The in-situ synthesized brazed product of claim 3, wherein the plurality of other layers surround the base layer when bonded.
 5. The in-situ synthesized brazed product of claim 3, wherein the product consists of the plurality of other layers and the base layer.
 6. The in-situ synthesized brazed product of claim 1, wherein the bonding of the base layer of the first material to at least one other layer of the second material is performed through a cold rolling process.
 7. The in-situ synthesized brazed product of claim 1, wherein the in-situ synthesized brazed product is heat treated after the base layer and the at least one other layer are bound.
 8. The in-situ synthesized brazed product of claim 1, wherein the first material of the base layer interacts with the second material of the at least one other layer when the base layer and the at least one other layer are heat treated at a temperature of 1200° Fahrenheit or less.
 9. The in-situ synthesized brazed product of claim 1, wherein the bonding of the base layer of the first material to at least one other layer of the second material is performed through a hot rolling process.
 10. The in-situ synthesized brazed product of claim 1, wherein the brazed product is further cut or formed into parts needed for the ultimate manufactured purpose.
 11. The in-situ synthesized brazed product of claim 1, wherein the brazed product forms a foil.
 12. A self-brazing alloy product, comprising: a. a base layer of titanium; and b. at least one other layer of copper, nickel, and/or zirconium, wherein the base layer is bonded to the at least one other layer, wherein upon brazing, some of the titanium of the base layer is extracted and interacts with the at least one other layer to form an in-situ synthesized brazed titanium alloy.
 13. The self-brazing alloy product of claim 12, wherein the titanium is extracted and interacts with the at least one other layer when the brazing ranges between approximately 1785° F. and 1992° F.
 14. The self-brazing alloy product of claim 13, wherein the at least one other layer comprises a plurality of layers, wherein the plurality of layers surround the base layer.
 15. The in-situ synthesized brazed product of claim 14, wherein the product consists of the plurality of other layers and the base layer.
 16. The self-brazing alloy product of claim 13, wherein the base layer is bonded to the at least one other layer through a cold rolling process.
 17. The self-brazing alloy product of claim 13, wherein the product is heat treated after the base layer and the at least one other layer are bound, the heat treatment done at a temperature at or below approximately 1200° Fahrenheit. 